SECT. II.]
PROPERTIES OF STEAM.
73
K
the lower ranges of temperature, and in the same manner as those on the force of
the steam of water; but in describing them it will be some advantage to begin
with the experiments of Cagniard de la Tour, on the space alcohol occupies when
converted wholly into vapour. To ascertain this point, alcohol of the specific
gravity '837 was introduced into small tubes of glass, and hermetically sealed,
with a handle of glass attached to each tube. A tube was two-fifths filled with
alcohol, and then slowly and carefully heated : as the fluid dilated, its mobility
increased; and when its volume was nearly doubled, it completely disappeared,
and became a vapour so transparent, that the tube appeared quite empty. On
leaving it to cool for a moment, a very thick cloud formed in its interior, and the
liquor returned to its first state. A second tube, nearly half occupied by the
same fluid, gave a similar result; but a third, containing rather more than half,
burst.
A process was next adopted to ascertain the pressure. It consisted in bending
a tube into a syphon, one leg to hold the liquid to be tried, and the other leg
containing air kept at a constant temperature of 73° by a cooling apparatus, and
separated from the fluid by mercury: both legs being sealed, the end containing
the liquid was heated, and when the liquid became vapour the diminution in the
bulk of the air was marked.
Alcohol of the specific gravity ‘837 w T as reduced into vapour at a temperature of
497° in a space a little less than 3 times its original bulk; and 476 parts of
air were reduced to 4 ; indicating a pressure, according to M. Cagniard de la
Tour, of 119 atmospheres, or 3570 inches of mercury. 1
105. The experiments on alcohol vapour at lower temperatures are collected
in the following table.
1 By the same process as was adopted in finding the constants for calculating the force of the
steam of water (art. 86.) the formula for the vapour of alcohol of sufficient purity to boil at
173° is
■ ■ -* ™ 6
or, in logarithms,
log. / = 6 (log. (t + 100) — 2 - 19000^);
where t is the temperature of the vapour, and /its force in inches of mercury. By this rule the
force for a temperature of 497° is 3280 inches : the experiment of M. Cagniard de la Tour
gives 3570 inches.